WordPress has released its newer version thats wordpress 2.6.5. Its an security fix and everyone using wordpress as their blog engine (most of you are) should upgrade to it immediately.
Wordpress has skipped version 2.6.4 as few “not so good” people had released a fake version of wordpress by this name. WordPress says “there had never been a wordpress 2.6.4 and there wont be any by that name”.
To download new version go to wordpress.org.